58 ON THE CAKAPAX AND STERNUM 



somite. From embryological evidence it appears very 

 probable that these pieces originate as simple projections 

 of the outer posterior angle ot" each sternal plate and that 

 they are apparently cut oil' by the appearance of false su- 

 tures at a later period of development. The figures illus- 

 trating this point (figs. 18, 19, 22) hardly need any 

 explanation beyond that given in the description of the 

 plates. A comparison of figs. 18 and 22 is conclusive. 



BIBLIOGRAPHY. 



1. Iluxley, T. H. Anatomy of Invertebrated Animals (chapter ou Crustacea). 



London, 1878. 



2. Milne-Edwards. Observations sur le Squelette Tegumentaire des Crustaces 



Decapodes et siir la Morpliologie de ces Animaux. Ann. Sci. Natiirelles 

 Ser. 3e, T. XVI, pp. 221-291. Pis. 8-U. Paris, 1851. Consult also Lemons 

 sur I'Anat. et la Phys., etc., T. 10, p. 212. Paris, 1872. 



3. Owen, R. Lectures ou the Conipar.ative Anatomy and Physiology of Inverte- 



brate Animals, p. 301. London, 1855. 



4. D.ana, James D. Homologiesof the Carapax among Crustacea. U.S. exploring 



expedition,]S38-'42, Vol. XIII, pp. 23-28, 32-35. Atlas, pi. 11, fig. 9d and 16, fig. 

 9c. Philadelphia, 18.52. Also On the markings of the carapax of Crabs. 

 Anier. Journal of Science and Arts, 2d Ser., Vol. XI, p. 95. (Jan., '51.) 



EXPLANATION OF PLATES II AND III. 



KEFERENCE LETTERS. 



a antennule n membranous space 



a' antenna o eye or orbit 



as antennular sternum os ophtlialmic sternum 



a's antennal sternum pg processes for attachment of gastric 



a't antennal tergum muscles 



a'<p plates of antennal tergum r rostrum 



ap appendage s sternum 



e epimeral plate sp sternal piece 



e' epimeral groove t tergum 



/ labrum tht thoracic tergum 



g plate covering green gland y suture between mandibular and 



g' plate between antennule and car- antennal sternum 



ai)ax X .«uture between epimeral and tergal 

 TO mandibular skeleton plates of mandibular segment 



mem membrane z point of attachment of carapax to 

 ms mandibular sternum body 



mt mandibular tergum 

 mp anterior mandibular epimeral 



plate. 



Fig. 1. Ventral view of carapax of an immature Platyonichus ocellatus, caustic 

 soda, acetic acid preparation; natural size. 

 Fig. 2. Ventral view of the earapax of Etiius dentatus; natural size. 



